Process for cooling and supporting a continuously cast metal bar

ABSTRACT

A process and apparatus for continuous casting of metal bars, in which the metal bar is formed in a cooled mould, extracted therefrom by roller trains, cooled during extraction and along its path of extraction the metal bar is subjected to the action of a fluid in an airtight chamber, the fluid having a pressure such as to compensate the hydrostatic internal pressure in the metal bar to reduce pressure and stress on the roller trains.

United States Patent 1191 Meylan 1451 Nov. 19, 1974 PROCESS FOR COOLINGAND 3,191,251 6/1965 OlSSOIl 164/283 s x SUPPORTING A CONTINUOUSLY CAST3,358,744 12/1967 Rossi 164/283 S X 3,596,706 8/1971 Knorr et a1.164/282 METAL BAR Jean-Luc Charles Meylan, Geneva, Switzerland Assignee:Battelle Memorial Institute, Carouge/Geneva, Germany Filed: June 8, 1972Appl. No.: 260,733

Inventor:

Foreign Application Priority Data June 9, 1971 Switzerland... 8423/71References Cited UNITED STATES PATENTS 7/1908 Trotz 164/283 R X PrimaryExaminer-R. Spencer Annear Attorney, Agent, or Firm-Waters, Roditi,Schwartz.& Nissen [57] ABSTRACT A process and apparatus for continuouscasting of metal bars, in which the metal bar is formed in a cooledmould, extracted therefrom by roller trains. cooled during extractionand along its path of extraction the metal bar is subjected to theaction of a fluid in an airtight chamber, the fluid having a pressuresuch as to compensate the hydrostatic internal pressure in the metal barto reduce pressure and stress on the roller trains.

7 Claims, 13 Drawing Figures PATENIE new 1 9mm SHEET 1 0F 4 FIG FIG. BO

PROCESS FOR COOLING AND SUPPORTING A E CONTINUOUSLY CAST METAL BARveying the steel strand thus obtained along and between two series ofrollers while it is being cooled until it has completely solidified. Thecooling is effected first by means of water jets and then by naturalheat radiation and convection. The path of the steel rod, whichinitially is inclined and curved, is gradually diverted into ahorizontal plane by the roller trains.

This process has, however, some disadvantages such 1 as it is necessaryto use a great many heavily loaded rollers, the apparatus required forcarrying out the process is heavy and bulky;

2. the life of the rollers is limited to but a few days;

3. the metal strand tends to bulge between the rollers due to the effectexerted by the hydrostatic (ferrostatic) internal pressure; the bulgingbrings about the well known metallurgical disadvantages such as fissuresand cracks, etc; in order to reduce the bulging a great number ofrollers is required; therefore, a great mechanical force is required tomove the metal strand;

4. the surface available between the rollers for cooling the metalstrand is limited;

5. the speed of movement of the metal strandis limited to about lm/min.

It is an object of the present invention to eliminate the aforementioneddisadvantages in a process for continuous casting of metal strands,particularly steel slabs, in which the metal strand is formed in acooled mould and extracted from the mould by roller trains, the metalstrand being cooled during extraction until it has completely hardened.To achieve this object, the process according to the present inventioncomprises subjecting the surface of the metal strand, in the region ofsolidification of the metal strand, along its path of extraction, to theaction of a gaseous medium having about the same pressure as theferrostatic internal pressure of the meta] strandthat at the same timesaid metal strand being cooled by spraying liquid on its surface.

Thus, the process of the present invention consists in counterbalancingthe hydrostatic pressure acting on the skin of the metal strand by thepressure of a gaseous medium located outwardly of the metal strand,instead of the rollers used for this purpose in the conventionalprocesses. Consequently, the rollers in the process of the presentinvention only serve as guide rollers and therefore their number andsize may be considerably reduced and they may be spaced further apart.The fluid pressure acting on the surface of the strand reduces thebulging between the rollers and therefore the force required for movingthe strand can be considerably reduced, particularly since the rollersare no longer subjected to the hydrostatic internal pressure of themetal strand, acting perpendicularly to their axes. Thereby roller wearis considerably reduced and their life is extended. This further permitsto increase their speed of rotation, resulting in an increase of thespeed of movement of the metal strand and consequently in an increase ofthe production capacity.

Although various gaseous mediums may be used in the process of thepresent invention, steam is most advantageous as it can be produced atthe desired pressure and at low cost by spraying water on the surface ofthe metal strand. Thus, for example, the heat emanated by a metal slabof30 X 200 cm, moving at a speed of l m/min., permits to produce about 15kg of steam per second.

Also air may be used as a gaseous medium although its use necessitatesthe employment of a compressor of a very high power. Also a mixture ofair and steam may be used, but such a mixture is less advantageous thanpure steam.

The process and apparatus of the present invention will now be describedin detail with reference to the accompanying drawings whichschematically show two embodiments of the apparatus with some variationsthereof and in which:

FIG. 1 is a longitudinal sectional view of a first embodiment of theapparatus;

FIG. 2 is a section taken on the line Il-ll of FIG. 1;

FIG. 3 is an illustrative diagram;

FIG. 4 is a part perspective view of a variation of the apparatus shownin FIG. 1;

FIG. 5 is a schematic longitudinal section of a variation of theapparatus shown in FIG. 4;

FIG. 6 is a schematic longitudinal section of another variation of theapparatus shown in FIG. 4;

FIG. 7 is a schematic transverse section through a particular embodimentof the injection device;

FIG. 8 is a plan view showing the elements of the injection device ofFIG. 7;

FIG. 9 is a sectional view, on a larger scale, showing a member of theinjection device of FIG. 7;

FIGS. 10, 11 and 12 are part longitudinal sections through the apparatusof FIG. 1, illustrating its operation, and

FIG. 13 is a longitudinal section through a second embodiment of theapparatus comprising only a horizontal portion.

The apparatus shown in FIG. 1 together with a cast metal slab 11comprises a conventional mould l of the type commonly used forcontinuous casting of steel slabs, a series of compartments 2a to 2gforming an inclined portion of the apparatus and separated from oneanother by parallel horizontal partitions, 3a to 3f, and a compartment4'separated from the compartment 2g by a horizontal partition 3g andforming a horizontal portion of the apparatus. Approximately in theircon tral portion the partitions 3a to 3g are provided with .an

aperture 33a to 33g-having the shape of the crosssection of the metalslab 11 cast and a size largerby a few millimetres than thiscross-section so as to provide some limited play for the passage ofmetal slab. The compartment 4 is closed at .its free end by a wall 5having an aperture provided with .an outlet seal 6 permitting the metalslab 11 to pass freely without any substantial leak of fluid fromtheinterior of the compartment 4 to the outside. The partitions 3a to 3gare spaced from one another by about 20 centimeters.

Rollers 9 are placed with their axes horizontally in the compartments 2ato 2g and the compartment 4 to guide and straighten the cast metal slab.The number of rollers 9 may obviously also be different from that shownin FIG. 1, and in particular it may be smaller than that shown, but atany rate it is smaller than the number of rollers in the conventionalapparatus for continuous casting of steel slabs. Each of thecompartments 2a to 2g is provided with at least two injection nozzles 10arranged substantially opposite each other on two sides of the metalslab 11. The number of injection nozzles 10 in the compartment 4 dependson its length, in the illustrated embodiment there are twenty.

Each of the compartments 2a to 2g is connected to the adjacent one by apressure control valve 14a to 14g. The compartment 2a is provided with afluid outlet aperture 13 provided with a control valve 13a.

In the illustrated apparatus the fluid utilized is steam produced insitu by injection of hot water through the injection nozzles 10 into thecompartments 2a to 2g and 4. The operation of the apparatus is asfollows:

By means of a casting ladle not shown in the drawings a jet 12 of moltenmetal, for example, liquid steel having a temperature in the order ofl,500 C, is cast into the mould 1. The steel slab flowing out of themould 1 traverses the apparatus shown in FIG. 1 from top to bottom andfrom left to right, cooling on its way and solidifying progressivelyfrom outside toward its inside. When the steel slab leaves the mould 1it is almost completely liquid apart from a thin deformable skin on itsouter surface and when it leaves the apparatus at the outlet seal 6 ithas completely solidified into an indeformable rigid block.

On the other hand, in the inclined portion of the apparatus the metalslab is mainly liquid. The portion of the metal bar located between thedash lines shown in FIG. 1 is the liquid pump inner portion of the metalslab.

In the compartments 2a to 2g and 4 the water injected through theinjection nozzles 10 is vaporized on contact with the metal slab 11 andwith the walls of these compartments to which some of the heat emittedby the metal slab is transmitted. In this manner in each of thecompartments 2a to 2g and'4 a pressure is produced which is equivalentto the hydrostatic pressure of the portion of the metal slab traversingthe respective compartment. The temperature of the metal slab in thecompartment 2g is in the order of 1,000 C and its hydrostatic pressureis about 5 to bars. In the compartment 2a the hydrostatic pressure ofthe metal slab is of the order of 1 bar. The pressure of the vapourincreases progressively from the compartment 2a to the compartment 2g soas to counterblanace the hydrostatic pressure of the metal slab alongits path through said compartments. The temperature at which the waterenters each of the compartments is adjusted to a value near the vapoursaturation temperature corresponding to the pressure required to prevailin the respective compartment, i.e., a value between 100 and 180 C. Inthis manner any undesired vapour condensation is avoided which mightoccur if an amount of water much higher than the amount of producedvapour were injected.

The diagram of FIG. 3 illustrates the internal hydrostatic pressure PHof the metal slab and the pressures of the steam (fluid) PF acting onthe metal bar in the various compartments 2a to 2g and 4 of theapparatus. As shown in FIG. 3, the steam pressure in each compartment isconstant and its value corresponds to the medium value of the internalhydrostatic pressure of the portion of the metal slab in the respectivecompartment.

The part perspective view of FIG. 4 shows a variation of the apparatusof FIG. 1, in which the space of the compartment 4 which is not occupiedby the metal slab 11 is longitudinally divided into two portions, i.e.,an upper portion 4a and a lower portion 4b, by a pressure loss device ordynamic joint formed by a plurality of horizontal partitions 8 which inthe illustrated embodiment are five in number and arranged around themetal slab 11 so as to form labyrinths 7. A by-pass pressure controlvalve 1411 (FIG. 5) connects the two portions 4a and 4b.

This variation permits to obtain below the metal slab a fluid pressuredifferent from that above the metal slab. Thus, by producing, forexample, below the metal slab 11 a pressure higher than that above themetal bar the latter is still better supported and guided and so thenumber of guide rollers can be further reduced.

The part view of FIG. 5 shows another variation of the apparatus withoutthe metal strand. In addition to the pressure loss device of thevariation described above, this variation comprises a steam recyclingsystem including a condenser 15 provided with a cooling fluid circuit16, a pump 17 and a conduit 18 for feeding the hot water produced by thecondenser 15 to the injection nozzles 10 (not shown in FIG. 5). Thearrows indicate the flow direction of the steam in the chamber and thatof the water produced by condensation of the vapour. The temperature ofthis water is in the order of C at the outlet from the condenser 15 inwhich the pressure is therefore slightly higher than atmospheric.

The apparatus shown in FIG. 6 is similar to that of FIG. 5, butcomprising additionally a second steam recycling system including avapour condenser 19 provided with a cooling fluid circuit 20, a pump 21and a conduit 22 for re-introduction of the hot water into theapparatus. A second control valve 23 permits vapour at high pressure tobe removed from the compartment 2g and to be introduced into thecondenser 19. The water at the outlet of the condenser 19 has atemperature of about C., whereas the temperature of the water at theoutlet of the condenser 15 is again 105 C.

The transverse section of FIG. 7 shows a compart ment of the apparatusprovided with a special type of water injection device formed byinjection pots 24 containing injection nozzles 25 connected through aconduit 26 to the source of water under pressure. The arrows indicatethe flow direction of the produced steam. The pressure of the vapour inthe pots 24 is higher than the pressure in the rest of the compartment.This injection device permits to improve the supporting and guiding ofthe strand and can be used either in all or only some of thecompartments of the apparatus. In the horizontal portion of theapparatus formed substantially by the compartment 4 this injectiondevice may be used, for example, only below the strand.

FIG. 8 shows the arrangement of the injection pots 24 with respect toone another. This staggered arrangement avoids the formation ofpermanent deformations in the skin of the strand. The injection pots 24may also have a different shape than that shown in FIG. 7, for example,a rectangular, oval or some other shape.

FIG. 9 shows an injection pot 24 provided with a rim 27 in the form of alabyrinth seal which permits to obtain a more progressive and regulardistribution of the pressure exerted by the water vapour on the surfaceof the metal slab 11.

FIGS. 10, 11 and 12 show the means used for setting the apparatus of thepresent invention into operation. For this purpose an articulated dummybar 28 is provided which at one end has a dummy bar head 29 with asurface corresponding to the cross section of the metal slab 11. Beforestarting operation of the apparatus, the head 29 closes the mould 1 asshown in FIG. 10. The other end of the articulated dummy bar 28 isconnected to appropriate means, not shovm, permitting to exert a pullingforce on the articulated dummy bar 28. In the lower portion of theapparatus, the articulated rod 28 passes along a channel provided in theinterior of a rigid rod 30 of the same cross section and weight per unitof length as the metal slab 11. The rigid rod 30 is likewise connectedto appropriate means, not shown, permitting to pull the rod 30 in thedirection of movement of the metal slab 11.

The apparatus operates in the following manner: Initially the apparatusis in the position shown in FIG. 10. Then the mould 1 is filled withsteel. The steel is allowed to form on its outer surface a skin which isthick enough to permit the slab 1 1 to be withdrawn. Then the slab 11 ispulled off while the mould 1 is supplied with a sufficient amount ofliquid steel. The pressure in the compartments 2a to 2g and thecompartments 4a and 4 l is adjusted to a value corresponding to that ofthe hydrostatic pressure of the head of the slab 11. Thus, in theposition shown in FIG. 11, the hydrostatic pressure of the head of theslab 11 in the compartment 2a is about 1.2 bars and the pressure in thecompartments 2a to 2g is adjusted to this same value of 1.2 bars. In theposition shown in FIG. 12, the head of the slab 11 has reached thecompartment 4a and pressure in the compartments 2a to 2g increases bysuccessive increments so as to counterbalance the hydrostatic pressureof the slab 11, the values of this pressure being, for example, 1.2bars, 1.4 bars, 1.6 bars, 1.8 bars, etc. Thus, the weight of the caststeel slab 11 in each compartment is compensated by the pressure of thefluid and the only force that need be applied is the force required toguide the slab 11 from one compartment to another. When the head of theslab ll arrives at the point of its path where the horizontal portionthereof meets the inclined portion,,the rigid rod 30 is moved whichhitherto has remained stationary and a difference in pressure isproduced between the compartment 4b and the compartment 4a, whichdifference is sufficient to lift the rigid rod 30 and thus the caststeel slab 11 and is produced by feeding into the compartment 4b a fluidunder pressure, for example, air or steam supplied respectively by acompressor or an auxiliary boiler, not shown. When the head of the caststeel slab ll arrives in the vicinity of the outlet seal 6, water isintroduced through the injection nozzles (FIG. 1) and the apparatus isoperated in the usual manner.

The embodiment of the apparatus shown in FIG. 13 has no curved portion.Instead of the mould 1 of the conventional type this apparatus has amould composed of a refractory ceramic portion 32 having no particularcooling means, and a portion 33 provided with cooling means. As avariation this embodiment of the apparatus may also comprise a pressureloss device of the type indicated by 7 and 8 in FIGS. 4 to 6. It mayalso be provided with a fluid injection device of the type shown inFIGS. 7 to 9 either on both sides of the cast metal slab 11 or only onits lower side.

The process and apparatus of the present invention may also be usedeither in only the inclined portion or the horizontal portion of thecast metal path with the other portion constructed in the conventionalmanner.

I claim:

1. A process for cooling and supporting a continuously cast metalstrand, particularly a steel slab, in which the metal strand is formedin a cooled mould and extracted from the mould by roller trains, themetal strand being cooled during extraction until it has completelyhardened, the improvement comprising subjecting the surface of the metalstrand, in the region of solidification of the metal strand, along itspath of extraction, to the action of a gaseous medium having about thesame pressure as the ferrostatic internal pressure of the metal strandand, at the same time, cooling said metal strand by spraying liquid onits surface, the metal strand leaving the mould being guided first alongan inclined and curved path and then along a substantially horizontalpath, the surface of the metal strand being subjected to the pressure ofthe gaseous medium increasing by steps along the inclined path, thevalue of the pressure in each step being substantially constant andcorresponding to the medium value of the ferrostatic internal pressureof the portion of the metal strand traversing said step.

2. A process for cooling and supporting a continuously cast metalstrand, particularly a steel slab, in which the metal strand is formedin a cooled mould and extracted from the mould by roller trains, themetal strand being cooled during extraction until it has completelyhardened, the improvement comprising subjecting the surface of the metalstrand, in the region of solidification of the metal strand, along itspath of extraction, to the action of a gaseous medium having about thesame pressure as the ferrostatic internal pressure of the metal strandand, at the same time, cooling said metal strand by spraying liquid onthe surface thereof and subjecting the lower surface of the metal strandto a higher pressure of the gaseous medium than the upper surface of themetal strand in a horizontal portion of the path thereof.

3. A process as claimed in claim 1 wherein said gaseous medium is steam.

4. A process as claimed in claim 2 wherein said gase ous medium issteam.

5. A process for cooling and supporting a continuously cast metalstrand, particularly a steel slab, in which the metal strand is formedin a cooled mould and extracted from the mould by roller trains, themetal strand being cooled during extraction until it has completelyhardened, the improvement comprising subjecting the surface of the metalstrand, in the region of so lidification of the metal strand, along itspath of extraction, to the action of a gaseous medium having about thesame pressure as the ferrostatic internal pressure of the metal strandat various positions'along said strand and, at the same time, coolingsaid metal strand by spraying liquid on the surface thereof, saidgaseous medium being steam produced by spraying hot water on the surfaceof the metal strand, the temperature of the sprayed water being near thevapour saturation temperature corresponding to the desired pressure.

6. A process as claimed in claim wherein the temperature of the sprayedwater is between 100 and 180 C.

7. A process for cooling and supporting a continuously cast metalstrand, particularly a steel slab, in which the metal strand is formedin a cooled mould and extracted from the mould by roller trains, themetal strand being cooled during extraction until it has completelyhardened, the improvement comprising subjecting the surface of the metalstrand, in the region of solidification of the metal strand, along itspath of extraction, to the action of a gaseous medium having about thesame pressure as the ferrostatic internal pressure of the metal strandand, at the same time, cooling said metal strand by spraying liquid onthe surface thereof in a direction opposite to the direction of movementof the latter, said steam being condensed to form hot water, and the hotwater being used to produce the vapor of the desired pressure.

1. A process for cooling and supporting a continuously cast metalstrand, particularly a steel slab, in which the metal strand is formedin a cooled mould and extracted from the mould by roller trains, themetal strand being cooled during extraction until it has completelyhardened, the improvement comprising subjecting the surface of the metalstrand, in the region of solidification of the metal strand, along itspath of extraction, to the action of a gaseous medium having about thesame pressure as the ferrostatic internal pressure of the metal strandand, at the same time, cooling said metal strand by spraying liquid onits surface, the metal strand leaving the mould being guided first alongan inclined and curved path and then along a substantially horizontalpath, the surface of the metal strand being subjected to the pressure ofthe gaseous medium increasing by steps along the inclined path, thevalue of the pressure in each step being substantially constant andcorresponding to the medium value of the ferrostatic internal pressureof the portion of the metal strand traversing said step.
 2. A processFor cooling and supporting a continuously cast metal strand,particularly a steel slab, in which the metal strand is formed in acooled mould and extracted from the mould by roller trains, the metalstrand being cooled during extraction until it has completely hardened,the improvement comprising subjecting the surface of the metal strand,in the region of solidification of the metal strand, along its path ofextraction, to the action of a gaseous medium having about the samepressure as the ferrostatic internal pressure of the metal strand and,at the same time, cooling said metal strand by spraying liquid on thesurface thereof and subjecting the lower surface of the metal strand toa higher pressure of the gaseous medium than the upper surface of themetal strand in a horizontal portion of the path thereof.
 3. A processas claimed in claim 1 wherein said gaseous medium is steam.
 4. A processas claimed in claim 2 wherein said gaseous medium is steam.
 5. A processfor cooling and supporting a continuously cast metal strand,particularly a steel slab, in which the metal strand is formed in acooled mould and extracted from the mould by roller trains, the metalstrand being cooled during extraction until it has completely hardened,the improvement comprising subjecting the surface of the metal strand,in the region of solidification of the metal strand, along its path ofextraction, to the action of a gaseous medium having about the samepressure as the ferrostatic internal pressure of the metal strand atvarious positions along said strand and, at the same time, cooling saidmetal strand by spraying liquid on the surface thereof, said gaseousmedium being steam produced by spraying hot water on the surface of themetal strand, the temperature of the sprayed water being near the vapoursaturation temperature corresponding to the desired pressure.
 6. Aprocess as claimed in claim 5 wherein the temperature of the sprayedwater is between 100* and 180* C.
 7. A process for cooling andsupporting a continuously cast metal strand, particularly a steel slab,in which the metal strand is formed in a cooled mould and extracted fromthe mould by roller trains, the metal strand being cooled duringextraction until it has completely hardened, the improvement comprisingsubjecting the surface of the metal strand, in the region ofsolidification of the metal strand, along its path of extraction, to theaction of a gaseous medium having about the same pressure as theferrostatic internal pressure of the metal strand and, at the same time,cooling said metal strand by spraying liquid on the surface thereof andin which the metal strand leaving the mould is guided first along aninclined and curved path and then along a substantially horizontal path,and whereby the surface of the metal strand is subjected to the pressureof the gaseous medium increasing by steps along the inclined path, thevalue of the pressure in each step being substantially constant andcorresponding to the medium value of the ferrostatic internal pressureof the portion of the metal strand traversing said step and wherein thesteam is conducted along the metal strand in a direction opposite to thedirection of movement of the latter, said steam being condensed to formhot water, and the hot water being used to produce the vapor of thedesired pressure.